ok I have what the shop told me is a 383 stroker crank BUT it has 383 and 355 punched into it So I measured it but i really don`t know how. This is how I did it, I measured from the center of the main journal to the top of the rod journal and it came out around 3.5" which to me says it`s a 350 crank because 350 cranks are 3.48", so did I do it wrong or is this crank a 350 and NOT a 3.75" 383 crank???? Please help,

Note: I read the notice about this tech page and it said stroker motors so I thought my question should go here, Sorry if I`m wrong this is the 1st time I`ve posted in here.

 

Actually the stroke is twice the "throw" or distance from the center of the main to the CENTER of the rod journal. The difference in throw for a 383 to a 355 is (3.75-3.48)/2 or .135 inches. You need a fairly accurate way to measure. If you can support the crank on 2 of its mains, like on a couple of parallel boards with v-notches cut in them, measure accurately from the top (outside) of a rod journal which is at it highest position. Note your reading, then rotate the crank to the lowest positon and measure to the highest part of the rod journal which is now the inside of the journal. A machinist's combination square is useful. Subtract the two readings, then subtract one half of a rod journal diameter or 1.05 inches. The result is the stroke.

Example: 7.0 inches top measurement and 2-15/32 lower measurement.
7.00 - 2.47 - 1.05 = 3.48. Or 7.0 top and 2-3/16 lower give 7.00 - 2.19 - 1.05 = 3.76 which would be a 383 crank.

I can't get 3.5 inches on either crank the way you described.

 

depending on the cranks manufactuer, sometimes it will have the stroke on it. both my eagle cranks have 383 on them.....

 

My crank which is a scat, has BOTH 383 AND 355 stamped on it

So I guess I measured it wrong, I just took a tape measure and put it 1/2 up the main journal and measured at the top of the rod journal which was a tick below 3.5"

 

Isn't that the [wrong] way that you described in the first post?
Measure center of main to center of rod journals and multiply that X 2